The present invention relates to a golf club head including a hollow portion therein.
Conventionally, importance has been attached to an impact sound of the golf club head. Particularly, the golf club head including the hollow portion therein is apt to produce a relatively great impact sound and hence, the quality of the sound is quite important. The current trend, in particular, is to reduce the thicknesses of individual parts of the head which is becoming larger and larger. Such a head tends to produce a low and loud impact sound, which is unpopular among most golfers. Therefore, it is quite important for the hollow golf club heads to produce an impact sound of proper volume and quality.
In this connection, there have been disclosed techniques for improving the impact sound. Japanese Unexamined Patent Publication No. 93559/2003 discloses a golf club head which includes a rib laid on an inside surface of a sole in a direction orthogonal to a face surface, such as to allow for the increase of the head volume relative to the head weight, thereby affording a comfortable hit feel as well as a comfortable impact sound.
Although not directed to the improvement of the impact sound, a technique of laying the ribs on the sole is proposed in Japanese Unexamined Patent Publication No. 313636/1995. The publication discloses a hollow golf club head which includes ridges formed on an outside surface of the sole as extended in the direction orthogonal to the face surface. The ridges are provided for the purpose of implementing a low centroid design and offering easy swing through.
Unfortunately, the above prior-art techniques have failed to fully improve the volume or quality of the impact sound. The vibrations of the sole upon impact with a ball are particularly great at an area near the face (an area adjacent to the face surface striking the ball). In the golf club heads of the above patent publications, the rib on the sole is extended from the area near the face surface toward a back side along a face-back direction. Therefore, the rib excessively suppresses the vibrations at the area near the face surface, so that the impact sound is excessively decreased in volume.
As a solution to this problem, it may contemplated to lay out the rib as follows. The rib is extended in a toe-heel direction rather than in the face-back direction and is located at place, for example, near the center with respect to the face-back direction rather than in the vicinity of the face. It is found, however, that this lay-out design cannot improve a low impact sound arising from a rib-free part of the sole although the rib is provided on the sole. The reason behind this fact is thought that the rib extended in the toe-heel direction and disposed near the center with respect to the face-back direction is located at a loop of sole vibrations produced at impact with the ball, thus acting to increase weight at the vibration loop so as to decrease the frequency of the vibrations. It is generally thought that the rib provided on the sole acts to increase the rigidity of the sole and to increase the frequency of the vibrations of the sole. However, the rib formed at the center with respect to the face-back direction as extended in the toe-heel direction has a relatively small effect to increase the frequency of the vibrations of the sole at impact with the ball. Rather, the rib has a relatively great effect to decrease the frequency of the vibrations because of the increased weight at the vibration loop.